1. Field of the Invention
The invention relates to joints for joining structural members, primarily those structural members made of wood.
2. Description of the Related Art
Wood is widely known to be an excellent building material. Compared to other building materials like steel and concrete, wood is is strong but light; machinable and durable; inexpensive and can be used for building by anyone who has access to the simplest of tools. It is therefore widely used to construct our houses and furniture.
Because wood is so widely used, the joints used in connecting structural members together are very important. Some of the most common joints are made by simply abutting the end of one structural member to the other. This type of joint requires other hardware--like nails, dowels or brackets--to hold them together. This is perhaps the most common type of joint used in home building and furniture making.
Another type of joint is formed by chamfering the ends of structural member, and securing them together somehow. Typically, the ends have to be glued or nailed together, or both. This is a common type of joint used in picture frames. The problem with this type of joint is that it does not withstand shear forces very well, and any force on the structure will impart shear forces on the joint. Glued joints of this type are weak, since glue does not withstand shear forces well. Nailed joints would tend to separate.
One solution that has been tried in the past is disclosed in U.S. Pat. No. 4,684,282, by Lever, that is not admitted to be prior art by its inclusion in this Background section. Lever discloses an interlocking joint with a mortise and tenon. However, the members are chamfered, and therefore result in shear stresses on the joint whenever force is put on the structure. This would tend to separate the members, and forms a relatively weak joint.
Another solution is disclosed in U.S. Pat. No. 5,848,852, by Shpigel, that is also not admitted to be prior art by its inclusion in this Background section. Shpigel discloses a strong joint, but one that is very complex to manufacture. He also requires addition hardware, like screws, in order to assemble the joint.
What is needed, therefore, and has not been found in the prior art is a joint in which shear force is not carried by glue; does not require extra hardware like inserts, dowels, screws, or brackets; is easy to produce with ordinary tools; and will accommodate either two or three structural members.